WASHINGTON—The Pentagon is assigning more special forces personnel to Yemen as part of a broad push to speed the training of the country’s counterterror forces in the wake of the failed Christmas Day attack on a crowded U.S. airliner.

Military officials familiar with the matter said the U.S. will begin rotating the same groups of special forces personnel through Yemen and keeping some of the elite troops there for longer tours, changes designed to help the American trainers develop closer relationships with their Yemeni counterparts.

The officials declined to specify how many new troops will be arriving in Yemen, but said it would be a significant increase above the roughly 200 special forces personnel who are currently in Yemen at any one time.

“The numbers are definitely going to grow,” said one military official familiar with the emerging plan, which is expected to be formally approved within weeks. “This will be a much more robust effort pretty much across the board.”